PROJECT SUMMARY Pregnancy is an important transition period that parous women (those who have given birth) undergo and it is linked to changes in risk of various diseases as compared to nulliparous women (those who have never given birth). The number of completed pregnancies changes the risk of autoimmune disease, Alzheimer's disease, cancers of the ovary, breast and liver, as well as asthma death later in life. However, it is unknown how these disease risks are altered by the child-bearing experience. DNA methylation (DNA-m) - the addition of a methyl group to cytosine in cytosine-phosphate-guanine (CpG) dinucleotides sequences in DNA - has been shown to be associated with multiple health outcomes later in life, such as atopy, eczema, hypertension, diabetes mellitus, and cancer. Our preliminary studies have shown that more CpGs (5.6% vs 0.7%) change levels of methylation during pregnancy (measured between age 18 years and again during pregnancy in women not yet pregnant at age 18) compared to pre-pregnancy (between ages 10 and 18 years), which may represent a plausible mechanism for altering post-pregnancy disease risks in parous women if these changes remain after pregnancy. To better understand the links between methylation changes during pregnancy and parous-related diseases later in life, we propose to identify pregnancy-related CpGs with significant pre- and post-pregnancy methylation changes through an epigenome-wide study. In Specific Aim 1, we will identify CpGs with significant methylation changes in parous women between ages 18 and 26-27 years compared to nulliparous women over the same time period. Then in Specific Aim 2, we will focus on the CpGs identified in Specific Aim 1 and test what proportion of them change from age 18 years to pregnancy and remain stable after parturition up to age 26-27 years. This proposed research has the potential to significantly contribute to 1) the discovery of biomarkers affected by a healthy pregnancy, 2) a better assessment of the long-term effects of parity on women in later life, and 3) the future development of epigenetic tools to detect these modified disease risks. Our collaborative research team is well-positioned to do this work with complementary expertise in genetics and epigenetics, reproductive epidemiology and (bio)statistics, and clinical medicine. We have a long track record of successful collaboration investigating DNA methylation changes during critical transition periods, such as puberty and pregnancy.